Apparition can be a full bodied or partial bodied ghost. A full bodied ghost is where you can see the entire body of a person. A partial bodied ghost is where you will only see part of the body like a head or the lower portion of the body. Sometimes you will see a ghost doing the same thing over and over, like always walking down a certain hallway or going up the stairs. This is done because that was something the ghost did in it's life and they are repeating it or reliving a moment in their life.
Poltergeists usually center their attention around one person. Most time these ghosts will be attracted to a person who is going through or are dealing with a lot of physical and/or emotional stress and/or anxiety. These are the ones that like to move objects, open and close doors, and knock on the walls.
Entities are creatures of divine or unearthly in nature and that they have not lived as human, for instances angels and/or demons. Usually feelings of overwhelming good ( angels ) or evil ( demons ) are associated with these.